The present invention relates to a negative resist composition suitably used in an ultra-micro lithography process, for example, the production of VLSI and high capacity microtips, and other fabrication processes. More particularly, it relates to a negative resist composition capable of forming high precision patterns using radiation, particularly, an electron beam or an X ray.
In processes for the production of semiconductor devices, for example, IC or LSI, fine fabrication has been conducted by means of lithography using a photoresist composition. In recent years, as the degree of integration increases in integrated circuits, it has been desired to form an ultra fine pattern in a submicron region or a quarter micron region. With such a trend, an exposure wavelength tends to become shorter such as from g-line to i-line or a KrF excimer laser beam. Further, the development of lithography using an electron beam or an X ray as well as the excimer laser beam also proceeds at present.
The electron beam lithography is regarded as the next generation pattern formation technique or the pattern formation technique after the next generation, and thus the development of a negative resist having high sensitivity and high resolution has been strongly desired. For the purpose of shortening the time for wafer process, it is a very important subject to increase the sensitivity of resist. In the negative resist for an electron beam, however, pursuit of the increase in sensitivity results in the degradation of line edge roughness and development defect property in addition to the decrease in resolution and the degradation of pattern profile. As a result, a problem of severe yield reduction of devices occurs. Therefore, it has been strongly desired to provide a resist composition satisfying these properties at the same time. The term xe2x80x9cline edge roughnessxe2x80x9d as used herein means a phenomenon wherein an edge between a line pattern of resist and a surface of substrate irregularly fluctuates in the direction vertical to the line due to the characteristics of resist, and the edge looks uneven when the pattern is observed from just above. Since the unevenness is transferred to the substrate in an etching step using the resist as a mask, the unevenness causes deterioration in electric properties thereby resulting in the yield reduction. A trade off relation between high sensitivity and high resolution, good resist pattern profile, good line edge roughness and good development defect property exists in the resist composition for an electron beam, and it is a very important subject to be solved that these characteristics are satisfied at the same time.
As a resist suitable for the electron beam or X ray lithography process, a chemical amplification resist mainly utilizing an acid catalyst reaction has been used in view of high sensitivity. In case of a negative resist, a chemical amplification composition containing an alkali-soluble resin, a crosslinking agent, an acid generator and other additives as main components is effectively employed.
With respect to improvement in characteristics of the chemical amplification negative resist, various investigations attending to the alkali-soluble resin have been made. For instance, the use of a resin containing a p-hydroxystyrene unit and having a narrow dispersity is described in Japanese Patent 2962145. The use of polyvinyl phenol having a low molecular weight and a narrow dispersity and a mixture thereof is described in JP-A-7-120924 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d). The use of a copolymer of hydroxystyrene wherein the hydroxy groups are partially esterified is described in JP-A-9-43837. The use of a mixture of a copolymer having a low molecular weight and containing a hydroxystyrene unit and a homopolymer of hydroxystyrene is described in JP-A-10-186661. The use of a copolymer of hydroxystyrene wherein the hydroxy groups are partially etherified is described in JP-A-2000-162773. The use of a polymer containing a hydroxystyrene unit having the hydroxy group in the 3-position is described in European Patent 1117002A1.
However, any of these alkali-soluble resins hitherto known cannot fulfill requirements for high sensitivity, high resolution, good resist pattern profile, good line edge roughness and good development defect property at the same time in the ultra fine pattern region.
Therefore, an object of the present invention is to solve the problems of performance-improving techniques in the ultra fine process of semiconductor devices.
Another object of the present invention is to provide a negative resist composition which fulfills requirements for high sensitivity, high resolution, good resist pattern profile, good line edge roughness and good development defect property at the same time in fine process of semiconductor devices using particularly, an electron beam or an X ray.
Other objects of the present invention will become apparent from the following description.
As a result of the intensive investigations, it has been found that the above-described objects can be accomplished by a chemical amplification negative resist composition comprising two kinds of alkali-soluble resins having specific structures, a crosslinking agent, an acid generator and a nitrogen-containing basic compound.
Specifically, the present invention includes the following negative resist compositions:
(1) A negative resist composition comprising (A-1) an alkali-soluble resin containing a repeating unit represented by formula (1) shown below, (A-2) an alkali-soluble resin containing a repeating unit represented by formula (2) shown below, (B) a crosslinking agent crosslinking with the alkali-soluble resin (A-1) or (A-2) by the action of an acid, (C) a compound that generates an acid upon irradiation of an actinic ray or radiation, and (D) a nitrogen-containing basic compound. 
In formula (1), A represents a hydrogen atom, an alkyl group, a halogen atom or a cyano group; and R1 and R2 each independently represent a hydrogen atom, a halogen atom, a hydroxy group, an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group, an aralkyl group, an alkoxy group, an alkylcarbonyloxy group or an alkylsulfonyloxy group, or R1 and R2 may be combined with each other to form a ring. 
In formula (2), A, R1 and R2 have the same meanings as A, R1 and R2 defined in formula (1) respectively, provided that the alkali-soluble resin (A-2) has the structure different from that of the alkali-soluble resin (A-1).
(2) The negative resist composition as described in item (1) above, wherein the alkali-soluble resin (A-1) contains a repeating unit represented by formula (1) and at least one repeating unit selected from repeating units represented by formulae (3), (4) and (5) shown below and/or the alkali-soluble resin (A-2) contains a repeating unit represented by formula (2) and at least one repeating unit selected from repeating units represented by formulae (3), (4) and (5) shown below. 
In the above formulae, 
represents a ring structure selected from the following structures: 
A has the same meaning as A defined in formula (1); X represents a single bond, xe2x80x94COOxe2x80x94, xe2x80x94Oxe2x80x94 or xe2x80x94CON(R16)xe2x80x94; R16 represents a hydrogen atom or an alkyl group; R11 to R15 each independently have the same meanings as R1 defined in formula (1); R101 to R106 each independently represent a hydrogen atom, a hydroxy group, a halogen atom, an alkyl group, an alkoxy group, an alkylcarbonyloxy group, an alkylsulfonyloxy group, an alkenyl group, an aryl group, an aralkyl group or a carboxy group; and a to f each independently represent an integer of from 0 to 3.
(3) The negative resist composition as described in item (1) or (2) above, wherein the crosslinking agent (B) is a phenol compound that has at least two benzene rings and does not contain a nitrogen atom.
(4) The negative resist composition as described in any one of items (1) to (3) above, which further comprises a surface active agent.